The use of a diagnostic apparatus using and ultrasonic wave for obtaining information on the internal parts of organs of a person is rapidly advancing. The marked progress of the image processing technique has permitted the utilization of an economical ultrasonic wave with low invasiveness and other superior characteristics as compared with the existing ones for diagnosis.
The ultrasonic diagnostic apparatus is widely known in either 1) A mode type method in which a wave reflected from an object is displayed as a waveform (i.e., a single position) on a cathode ray tube or 2) B mode type method in which a single, obtained by an A mode method and subjected to intensity modulation, is used to scan a transducer thereby to display a section (i.e., a plurality of single positions from the A mode method) as an image.
The ultrasonic diagnosis for ophthalmology is generally divided into a basic examination, intended primarily for screening, and a special examination for analyzing the essential conditions of a morbid part or differential diagnosis. The special examination is further subdivided into i) a morphological differentiation for locating an affected part and determining the area covered except for more dynamic affected parts, and ii) a tissue differentiation for identifying the cause of the morbidity.
The B mode method is more widely used in the medical field. In ophthalmology, however, a method of tissue differentiation by a A-mode method is more established and developed than by a B-mode method and therefore both methods are used in combination taking advantage of the respective merits thereof.
The A-mode method permits determination of the acoustic characteristics of a focus by high or low response of a reflected wave as well as measurement between different tissues in the eye. In the tissue differentiation by the A-mode method of the conventional apparatuses, complete image processing is difficult, and therefore the minimum decibel value (dB) necessary for a spike from the morbid part to reach a mark line of a predetermined height is determined by changing the gain (also called the sensitivity) of an amplifier. Then the minimum decibel value of a spike from the sclera, which protects and holds the shape of the eyeball, is determined, so that the morbidity is estimated from the difference (.DELTA. dB) between the two decibel values.
The B-mode diagnosis that has come to be widely used by ophthalmologists is useful for determining the range and size of a morbid part or anatomical morphological decision. The B-mode diagnosis of the conventional apparatuses requires a plurality of B-mode images for more three-dimensional tissue differentiation and employs a method in which each image, obtained by changing the sensitivity of the amplifier, is photographed by a Polaroid camera from Polaroid Corporation, U.S. or the like.
In view of the fact that the ultrasonic diagnostic apparatus for ophthalmologists is operated with an ultrasonic probe applied directly to the cornea of the patient under local anesthesia with the patient's lids retracted, a protracted diagnosis time imposes a heavy burden on the patient's. Further, the poor reproducibility of the apparatuses requires considerable skill on the part of the operator.